Dovecot - is there any way to define a single root directory and all others as subdirectories?

Hoping someone can shed some light on this for me. I'm currently migrating our mail service from Dovecot to Office 365 Exchange Online. The IMAP migration fails as it states there are too many root directories.

I spoke to Microsoft support today and they suggested that my directory structure would be something like;

Inbox (root) Sent (root) Outbox (root) etc

So when migrating by IMAP it sees multiple root directories defined and throws an error.

Obviously I'd like to be able to change this to have Inbox as the main directory and all others as subdirectories.

Hopefully this makes sense to someone, the only other thread I can find discussing the error I'm getting is here https://www.reddit.com/r/exchangeserver/comments/5y8x4j/exchange_migration_issue_imap_to_exchange/